i have the same phone! i been got it when it first came out so i know all about it! its called threaded text messaging. i looked all in the text messaging setting, i looked everywhere, you can not get that on ur phone (our phone). sorry! i don't have a problem with it though. but there is alot of things/feature you can do with the solstice. like.... when ur sending a picture (if u have picture messaging) you can put it as a slide show or u can change the background color and the handwriting! and when ur taking a picture you can change it, edit and do much more! i love this phone! there is more things u can do with it to. just pick it up and explore
good luck!